25. Solving a chemistry problem

3. 10 ml of wastewater was placed into two 50 ml volumetric flasks. 5 ml of a standard solution with an iron (III) titer of 0.0013 g/ml was added to the first flask. Then, reagents to obtain light-absorbing particles were introduced into both flasks and diluted with water to the mark. During photometry, the following data were obtained: the optical density of the solution from the first flask is 0.540, the optical density of the solution from the second flask is 0.360. Determine the concentration (g/l) of iron in wastewater.